Acoustic translating device



A. F. SYKES ACOUSTIC TRANSLATING DEVICE- 5 Sheet-Sheet 1 Filed March 13,1935 4 mvw 03 f April 28, 1936. F SYKES 2,038,687

ACOUSTIC TRANSLATING DEVICE Filed March 13, 1935 5 Sheets-Sheet 2 5Sheets- Sheet 5 Filed March 13, 1935,

28, 1936. A. F. 'SYKES 2,038,687

ACOUSTIC TRANSLATING DEVICE 5 Shets-Sheet 4 Filed March 13, 1955 A. F.SYKES 5? ACOUSTIC TRANSLATING DEVICE Filed March 13, 1955 5 Sheets-Sheet5 a records.

Patented Apr. 28, 1936 UNITED STATES ACOUSTIC TRANSLATING DEVICE AdrianFrancis Sykes, St. Albans, England Application March 13, 1935, SerialNo. 10,922

In Great Britain March 15, 1934 16 Claims.

This invention relates to acoustic translating devices and morespecifically to devices for trans lating sound frequency electriccurrents or voltages into: mechanical movements for recording gramophoneor phonograph records and to devices for translating recorded gramophoneor phonograph records into sound frequency electric currents orvoltages. Translating devices of the former type are generally termedrecording devices and devices of the latter type are generally termedpick-up devices.

Talking machine records as commonly used hitherto fall into one or otherof two classes ('1) gramophone records and (2) phonograph In the formerclass what is termed lateral cut is employed, i. e., the sound wave formrecorded is lateral so that the recorded groove is a wavy groove withwaves at right angles to its general direction while in the latter classwhat is termed hill and dale cut is employed, i. e., the depth of thegroove is varied in dependence upon the acoustic waves recorded. Thepresent invention is applicable to talking machine pick-ups andrecorders for picking up from or recording records of either class.

The usual practice in present day design of talking machine pick-ups andrecorders isto make the armature which carries the pick-up or recordingstylus (as the case may be) as rigid as possible so that it vibrates asnearly as possible as a whole. Almost always the said armature will haveat least one resonance within the acoustic frequency range to be handledand it is usual to avoid (so far as is possible) disproportionateresponse at and near such resonances by providing damping material suchas rubber, to bear upon the armature at some suitable point or points inits length; e. g. in the case of a pivoted armature, the pivot may besurrounded by damping material. Pick-ups and recorders so designed,however, leave much to be desired in the matter of uniform response overa wide frequency range and sensitivity and although, by very carefulmanufacture it is possible to obtain fairly uniform response over areasonably wide acoustic frequency range, known pick-ups and recordershave had to be made undesirably'expensive in construction if they are tobe both insensitive and able to handle a wide range of frequencieswithout appreciable distortion.

The main object of the present invention is to avoid the difficultiesand disadvantages hitherto met with in known talking machine pickups andrecorders and to provide improved pickups and recorders of simple andcheap construction, good sensitivity and high fidelity over a wideacoustic frequency range.

In: accordance with this invention the'above mentioned general principleof design is dis-- carded and instead there is employed an arma- 5 turewhich is sufliciently flexible to have sound frequency waves set uptherein. This armature is so mounted that the sound energy to berecorded or picked-up (as the case may be) causes sound wave fiexure tooccur with the particle displacement at right angles to the direction oflengthof the, armature (i. e., the armature has transverse or bending ortwisting sound Waves set up therein as distinct from tension andcompression waves) and the waves thus set up in the armatureare dampeddown by rubber or like material which is held in contact with the sidesof; the said armature over a substantial portion (at least half) of itslength, the movements of the undamped end of the armature beingutilizedfor recording 'or for generating electric waves (as the case may be) andthe said armature bei supported solely through the intermediary of thedamping material.

The necessary translation of electric waves into mechanical movements ofthe undamped end of the armature (for recording) or vice versa (forpicking up) may be accomplished in any manner well known per se; forexample the end of the armature may extend into an air gap of apermanent; magnet and be itself of ferre -magnetic material so thatmovement of the said end varies the gap and thus induces currents in acoil wound about a limb of the 'magnet while conversely currents fedtothe coil will cause 5 movement of the said end; or a balanced'magnet'system may be used and the end of the armature arranged between thepoles thereof; or the end of the armature may project into a gap in amagnetic system and beitself 'surrounded'by a 40 coil in which currentswill be induced by movement of the said end or vice versa. As these andother forms of associated'magnet systems are all well known, per se, inpick-up and recorder practice, and form, per se, no part of the presentinvention, it is not thought necessary to describe them individuallyfurther herein. In this connection it is to be understood that any ofthe embodiments of the invention to be hereinafter illustrated anddescribed.- may be modified by substituting any known means (other thanthose shown) for translating movements of the armature end into electriccurrents or voltages or vice versa. Also all those illustratedembodiments which are adapted for Working with phono-cut (and viceversa) could be modified for working with gramophone out merely byre-arranging the stylus or the like to take into account the differentdirections of the cut.

The invention is illustrated in the accompanying drawings in which:

Figures 1, 2 and 3 are respectively an elevation in part section, a planfrom beneath and a plan from above illustrating an electromagneticpickup, suitable for use with a cylinder phonograph with a feedcarriage-such for example as the well known Edison'standard phonograph.

Figure 4 is a view of the end of the polar extension 5 of Figures 1 to 3showing the U shaped wire 2|, the bobbin 9 in section and the chamferedcylindrical pole ll.

Figures 5, 6 and 7 are views in part sectional elevation, top and bottomplan respectively of a pick-up for use with phonographs of thetravelling mandrel type.

Figure 8 'is a plan view of the armature 7 of Figures 5 to 7 and.

. Figure 9 shows a detailmodification which consists in replacing therubber strips l2 of Figures 5 to- 7 by a rubber tube 47.

Figures, 10 and 11 are respectively a view from above and a sideelevation of a pick-up used with the tone arm of a .goose-neckgramophone.

Figure 12 illustrates a form of the invention as applied to the wellknown Edison diamond disc phonograph.

a moving coil.

, Figure 14 is a. circuit diagram.

Figures 15 and 16 are a side View and a plan of an embodiment of theinvention as fitted to an Edison diamond B reproducer.

Figure 17 illustrates the pick-up movement proper of Figures .15 and 16.

Figure .18 shows an alternative method for hold- 7 ing the. armature ofFigures 15 to 17.

Figures .19, 2.0 and 21 are respectively a view from above, a. viewfrombeneath, and a View in part section of another embodiment. In Figure 19the floating weight depicted in Figure v21 is omitted as is also thecase in regard .to Figure 20.

Figure -22 illustrates the method of polar adjustment used in Figures 19to 21 but is not to scale, being merely explanatory- Figure 23 shows a'preferred way of forming a driving cord such .asthe transmission deviceor cord of Figures 19 to 21. 1

, Figures 24, 25. and 26 represent respectivelyan elevation in partsection, a plan from beneath and an end view respectively of anembodiment of the .invention as applied to the conversion of an existingmechanical reproducer to act as an electric pick-up. V

Figures 27 and 28 show respectively a face view .with cover removed anda side external view of a pick-up embodying the invention and adapted tooperate with lateral cut records.

. Referring first to Figures 1 to 3,! is a shell or housing moulded e.g. from the material known under the registered trade-mark Bakelite andprovided with a threaded bush 2 in which is screwed so as to be freelyrotatable therein, a

screwed stud 3 which provides for the requisite freedom of. movement forthe pick-up move-' ment proper. The magnetic structure of this movementcomprises a fifteen per cent cobalt steel bar magnet 4 with slottedpolar extensions 5 and 6 and an armature I cut from hacksaw. steel 0.025inch thick, to which is soldered the brass holder 8 of the diamondstylus normally provided in Edison standard phonographs. A bobbin 9 andwinding I0 is friction tight on the cylindrical portion H of the polarextension 5. The armature 7 is clamped in position between rubber stripsI2 by a copper plate l3 through which pass four screws which enter thepolar extension 6 as .at 14. By adjusting these screws the degree ofclamping can be adjusted. A small bar 15 enters a slot in the polarextension 6 and a pin or axis l6 passes through the said bar so that thepolar extension 6 and the bar l5 can pivot relatively to one anotherabout the axis 15. The other end of the bar I5 is clamped'to therotatable stud 3 by the screw ll. Fine wire leads l8 which arepreferably coiled as shown extend from the ends of the coil or windingII] to terminals l9 and 20. A bent U shaped wire 2| pressed into holesin the extension 5 engages with a limit stop 22 and thus limits themovement of the pick-up proper relatively to the housing I. A splitstrut 23 tightened by the screw 2e serves to brace together the magneticstructure. The housing I is turned at 25 to a diameter of approximatelytwo inches to fit the normally provided ring of the feed carriage of anEdison standard phonograph and is counterbored inside up to the line 23to provide'clear gated slot 27. The housing I is chamfered sufficientlyat 23 to allow the instrument to remain in the phonograph with the usualdust cover in place and is recessed as at 29 to protect the junction ofthe fine wire connections with the ter! minals. A small depressionregisters with a pin on the normal Edison feed carriage to secure readylocation. About 5300 turns of wire are wound on the bobbin giving aresistance of 1000 or thereabouts, but, of course, if required e. g; ifa transformer is tobe used with the pick-up a so-called low resistanceco-il canbe used. As previously stated Figure 4 is a view of the end ofthe polar extension 5 of Figures 1 to 3 showing the U shaped wire 21,the bobbin 9 in section and the chamfered cylindrical pole il. Figures5, 6 and 7 are views in part sectional elevation top and bottom planrespectively of a pick-up for use with phonographs of the travellingmandrel type. Here a hexagon rod 3i is screwed into a larger hexagonmember 32 turned as at 33 so as to enter the reproducer post 34 which isindicated 7 by the dotted line circle. A bracket 35 swivelled (invirtue-of the screwed stud shown) about the axis 35 supports the housing31 which is slotted at 38 to receive and clamp the pick-up mechanism bythe screw 39 in adjustable relation. Brass bushes 40 are inserted tomaintain a slight clearance between the limbs of the bracket and the 1housing. The bracket supports the housing by a pin I6 so that it is freeto move about the axis.

associationwith the U shaped wire 43 and a bent strip of metal 44attached by a screw 45 engages with the lowering mechanism shown dottedat 45. The actual pick-up differs from that of Figures 1 to 4 only byreason of the horizontal positioning of the magnet as in is notrestricted by the limitations of an already existing feed carriage.Figure 8 is a plan or the armature 1' and Figure 9 shows how the rubberstrips l2 can conveniently be replaced by a rubber tube 41. Ripples ofvibration in the armature are absorbed in the damping (l2 or 41 as thecase may be) as they travel along the armature and any reflected ripplesfrom the end of the armathis case the design ture are similarly damped.As the armature does not touch the polar extension 6 the magneticcontinuity is obtained by the large area air gap separating the armatureI from the polar extension 6. The gap between the armature and the woundpole tip is not of a minute order and the vibration from the record isonly a small fraction of this dimension, consequently the adjustment isnot critical. In a. practical example constructed as shown in Figures to'7 the weight on the diamond point was about two ounces and a quarter asagainst about one ounce and a quarter for an actual pick-up constructedas illustrated in Figures 1 to 4.

Figures 10 and 11 are respectively a view from above and a sideelevation of a pick up used with the tone arm of a goose neckgramophone. In this case an instrument of the type shown in detail inFigures 5 to I is screwed to the bifurcated member 48 by the screw 49and a screwed pin 50 clamps the member 48 to a trunnion 51 with justsufiicient clearance to permit free up and down movement. As shown thearmature is equipped with a stylus holder 53, tightening screw 54 andweb 55 arranged for a needle stylus (as shown) or for a diamond tippedstylus. This instrument when equipped with a diamond can reproduce e. g.from the well known Edison diamond discs or, by changing to a steelneedle it can reproduce from a record such as that described and claimedin my British Patent No. 303,759. The weight on the point was, in apractical example, just over three ounces.

Figure 12 illustrates a form of the invention as applied to the wellknown Edison diamond disc phonograph.

A cylindrical portion 33 with registration pin 56 is provided to enterthe reproducer post (not shown). To this portion is attached, as forinstance by silver soldering, an arm 3 5, either solid or as a shell,hinged at 51 with hinge pin 58. This arm supports the pick-up housing asshown in a manner very similar to that of Figure 5 except that in thiscase the requisite two degrees of freedom are obtained by means of atrunnion 59 set between pivot screws as at 60 within the recess BI andthe screwed stud 3 (as in Figure 1). The function of the hinged arm 3|is to allow the pickup to be swung up for changing a steel needle or foradjustment. Where reproduction is to be effected only by a permanentjewel provision for allowing such swinging up is more or lesssuperfiuous.

Figure 13 shows an embodiment generally similar to those alreadydescribed but using a moving coil. Here the polar arrangement takes theform of the widely known annular magnetic gap with circular coil locatedtherein. A coil drive element 62 is riveted to the armature holder 1which may or may not be metallic.

Figure 14 is a diagram showing a shaping and control circuit comprisinga resistance 63 across the pick up a condenser 64 variably tapped uponthe resistance 63 and a potentiometer resistance 85 acting as a volumecontrol. The pick-up terminals are connected to the lower terminals inFigure 14 and the input terminals of the reproducer amplifier areconnected to the other terminals in Figure 14. It is found in practicethat with pick-ups as abovedescribed the upper audio range issufficiently strongly reproduced as to be regarded as excessive whensuch a pick-up is used in conjunction with an ordinary moving coilloudspeaker. Hence it is desirable to load the pick-up by the resistance63 which may take the form of a graphited surface and may be of theorder of 50,000 ohms for use with an instrument as described withreference to Figures 1 to 4. The action of the resistance load can besupplemented to a desired extent by the condenser 64 which may have acapacity of the order of 0.01 microfarad for example.

Instead of an armature of the type illustrated I may find it desirablefor some purposes to adopt the general principle ofthe double poletelephone receiver and allow a small piece of iron attached toanarmature holder to bridge the magnetic gap. The holder of the armaturewould be sup ported and disposed in'a manner similar to that describedfor the member 1 illustrated.

Furthermore I may use an armature as illustrated but set betweenmagnetic poles, the armature acting as a magnetic potentiometer fingerbetween the fiux in the magnetic gap and the neutral section of themagnet with a winding en'- circling the armature or central magneticpath. In any event the armature would be impulsed as above described 1.e. in the immediate vicinity of the poles. For phonocut records eitherdisc or cylinder the vibration could be transmitted by the floatingweight method with cord and lever as well known per se, while forordinary gramophone records a short stylus or semi-permanent type couldbe set in a local thickening of the armature.

Figures 15, 16 and 17 relate to a pick-up designed to operate inconjunction with an'Edison phonograph. As will be seen, in thisembodiment, substantially all the parts of the existing reproducer withthe exception of the diaphragm are utilized, but the top of thereproducer shell, principally the short tubular portion communicatingwith the normally provided horn, is cut away, and on the reproducershell so modified is mounted an apparatus in all essential particularsidentical with the floating pick-up illustrated in Figure 5 above.

Referring first to Figures 15 and 16 the reproducer comprises as mainparts a shell 66, floating weight 61 and stylus lever 68. The top of theshell is cut away and the central hole suitably enlarged or trimmed upto bed the pick-up housing 31 with cover'll which are both moulded e. g.in the material known under the registered trademark Bakelite, or inebonite. This housing has protuberances 69 to accommodate screws Hi forsecuring the housing to the reproducer shell. A screw 39 clamps themagnetic structure of the pick-up in adjustable relation to the housing.This magnetic structure is indicated in. dotted fashion in Figures 15and 16 but is shown more fully in Figure 17. Terminals'lS communicatewith the coil 10 of the pick-up. The housing may be made in halvesjoining along the centre line H in which case the top or lid may beformed in the moulding if desired. The pick-up movement proper (seeFigure 17) consists of a cobalt steel magnet 4 a polar extension 6 awinding i!) on a suitable bobbin, an armature I clamped between rubersheets as at l2 or alternatively set in a rubber tube, a clamping plateI3 of copper or German silver and four screws as at M for attaching andadjusting the plate. At or near the end of the armature I is soldered abrass crosshead 12 to which is attached the loop of thread 13 knotted at14 engaging with the stylus lever 68. The magnetic vflux passes into thearmature by the'largearea leakage path.

Figure 18 shows an alternative method for holding the armature ofFigures to 1'7. Here the chamfered end of the armature 1 (the armatureitself is set in a tube of rubber or folded sheet 41 corresponding tothe rubber l 2 of Figure 17) is ripped in the sheet iron holder 15 witha suitable number of holding down tabs as at is pressed out of thematerial itself and adapted one eighth of an inch. These figures arepurely illustrative and are capable of considerable variation; e. g. anarmature ofabout two-thirds the stated thickness 'or of about half thestated width may be used with apparently beneficial results as to theefiiciency of the damping material (IE or 47). For reproduction from waxrecords it may be found desirable to adopt even smaller values and wherenecessary use a great degree of electrical amplification. Reducedthickness apparently allows the ripples set up in the armature to bespaced closer together for a given frequency and perhaps thereforecontributes to the eificiency of the damping channel. This method ofdamping employed (contrary to sound-box practice) provides a muchextended'length of damping path. The waves or ripples set up apparentlytravel the length of the armature, are reflected from the end and returnalong the armature in attenuated form. It is found that the smallerarmatures with a given transmission link :13 (e. g. cotton) require acondenser of greater capacity to counteract the enlargement of the highfrequencies. It may be desirable to use one of theimproved magneticsteels as the material for the armature.

Reproducers with floating weight have been constructed wherein the forceexerted by the weight is increased or supplemented by the action of aspring. In this case the floating weight is generally lighter and thepractice tends to help in the reproduction from cylinders which are nottruly round. Sucha method obviously can be applied to the practice ofthe present invention. It is found that the casual deformities existentin celluloid cylinders in greater or less degree show up in the electricreproduction, as bumping noises, to a much aggravated extent owing tothe more adequate response in the bass register. To counteract thisdefect where necessary or desirable I may insert a series condenser inthe pickup leads in conjunction with a shunt resistance (of say: 50,000ohms) acting as a volume control and to reduce the bass response.Another method is to insert a small pad of rubber between'the armatureand the bobbin which tends to render the elastic action of the armatureless extensive and thus throws the adjustment to lowfrequencydeformities more on the inertia of the floating weight. This electricreproducer can also be used to reproduce from disc records of phono-cuttype.

The armature could, of course, be arranged to work between poles on apush pull basis as well known, per se, but it is notthought that muchwould be gained by this complication in view of the small amplitudesnormally prevailing. V

producer shell and replace by a suitable moulded modification. V V 7Figures 19, 20 and 21 show a construction in which a moulded shellcomprises a rectangular hollow portion 78, a circular flange 19 nearlycomplete but cut away to correspond with the internal recess or slot 80of the portion 18 and a tail piece 8| which serves to support theconventional, and well known, floating weight system on Edisonphonographs. This tail piece projects below the bottom of the recess asabove by about five sixteenths of an inch. A projection 2| integral withthe moulding acts as a limit pin for the loop of the floating weight.The electromagnetic mechanism is closely similar to that illustrated in.Figures 15 to 17. It consists of a cobalt steel magnet 4, a polarextension 6, a winding l 0 on a suit-- able bobbin, an armature 1clamped between rubber sheets as at I 2 or alternatively set in'a rubbertube, aclamping plate I3 of copper, German silver, or iron, and fourscrews as at M for attaching and adjusting the plate. At or near the endof the armature 1 is soldered a brass crosshead 12' to which is attachedthe loop of thread, twisted or otherwise, wire link, cord or othertransmission device engaging with the sty-' lus'lever 68. The magneticflux passes into the armature by the large area leakage path and theplate i 3 allows the degree of restraint and amount of damping to becontrolled. It, that is to say the plate, further permits the polar gapto bevaried in the absenceof or in conjunction with any other form ofadjustment. The terminals I 9 are connected to brass laminae as at 82 tofacilitate soldering'of the connections. 7

A ridge is shown on the bobbin for anchoring in holes the fine wires andin Figure 21 this ridge or edging is partly cut away so as not toobscure 84 support the electhe drawing. Nuts 83 and tromagnetic systemwithin the housing. Dis

tance washers as at 85 provide an element of ad- 7 justment and thesemay be of metal or say vulcanized fibre. I may find it desirable to usesoft washers both top and bottom to insulate acoustically to some extentthe electromagnetic mechanism from the shell. and diamond tipped styluslever 68 as depicted are representations of existing products and hencethe invention while complete in itself is particularly adapted as anattachment for the conversion of existing machines; all that isnecessary is for the shell or sound box of the reproducer as used formechanical reproduction to be' removed and replaced by the shell andassociated mechanism as described. A cap 86, which may be of brass,engages with the central core of the pole and enables this to be rotatedby hand and so vary the magnetic gap.

Figure 22 shows the central pole l i fashioned as a sleeve and providedwith a kind of shoulder as at $7. The central core 88 is a sliding fitbut both this coreand the sleeve i l are screwed at the top end so thatrotation of the core causes a traversing movement. If desired the top ofthe-core 88 in- The floating weight 51 stead of being squared andtapped'for the attachment of the cap 86 may simply be slotted foroperation by means of a brass screw driver and a lock nut provided forlocking it in position.

An important subsidiary feature of Figures 19-22 lies in the method ofpole adjustment whereby the central core of the pole is traversed by ascrew feed and thus facilitates assembly and can function as a volumecontrol in use.

Difi'iculty may be sometimes met with in the pick-ups so far describedby undesirable resonant notes or periods of vibration set up bymechanical transmission of sound from the record being reproduced. Toprevent this a pad of rubber, insertion, cork or other damping material(not shown) may be placed between the pick-up movement proper and thecasing in any of the embodiments illustrated so that there is dampingmaterial between pick-up and casing. For example, where nuts are used toclamp the pick-up to the top of the casing the clamping action maycompress an interposed rubber pad over the length of the magnet. Thus asecure fixing is provided and also an agency acting in restraint ofresonant vibration. In another method (not illustrated) the pick-up iswrapped with a rubber sheet covering the sides and also the top, withholes to clear any nuts or projections, and the pick-up so wrapped isforced into a slot in the housing. This also is a practical andcomparativelyefiective procedure which has the advantage of insulatingthe mechanism from external shocks.

Preferably in embodiments, (see for example Figures-l9 to 21) where thelink connecting a stylus lever with the armature is of a cord nature thesaid link is fashioned from a series of slipping loops pulled tight asthe threading of the cord (usually a silken cord) proceeds so that thereis a sort of chain stitch effect as illustrated in Figure 23 which ispurely schematic and not to scale. The final loop, for attachment to theback of the stylus lever, is left comparatively open and locked bystitching to the preceding loops or binding over. On thearmature thecommencing thread of the loop system is passed through the hole in thecross head and tied. Alternatively the cross head soldered to thearmature may be adapted to grip the silken cord, and, if the length isapproved on trial, made secure withshellac or other c'ement. In somecases I have found it advantageous to make the cross head of anelongated nature, resembling a web, thereby increasing the stiffness ofthe armature where it is not gripped by the combined rubber support anddamping means.

The object of the chain knotted type of cord transmission link is toprovide an element of damping in the connection between the stylus leverand the armature and thus minimize resonant'vibration' of a relativenature between these parts.

In the embodiment shown in Figures 24 to 27 the reproducer shell 89 ofan Edison disc phonograph is shown as stripped of its normal floatingweight, stylus lever, transmission cord, and diaphragm. V For theseparts are substituted a moulded floating weight 90 carrying a magnet 4,magnet cores I I, windings l0, polar extensions 6, armature I withstylus 8 soldered thereto, clampin'g plate 13, rubber sheets or tube l2,and terminal screws l9 which connect with the windings.

The moulding 99 is channelled as at 9| and the clamping plate I3 istightened with screws as at 14 until it touches the ledge 92 of thechannel 9|. This arrangement secures uniformity of compression inassembly and thusuniformity of damping per unit length. However if it isdesired to use the clamping plate as a means for regulating the degreeof proximity of the armature and the poles the ledge can be omitted. Inthe arrangement shown the polar gap can be adjusted in manufacturingassembly with the aid of paper washers or shims placed beneath therubber of the damping channel or it can be adjusted in other ways e. g.by straining the armature. armature shown is one eighth of an inch wideand one thirty second of an inch thick and is made of soft tool steel.

Figure 27 shows in front elevation with cover removed and Figure 28shows in side elevation a pick-up constructed for reproducing fromlateral cut or gramophone records. In this pick up there is a compositemagnetic framework comprising magnets 4, polar extensions 6 combining toform a single neutral region, and pole tips I I tapered as shown andwhich provide magnetic air gaps on both sides of the armature l. Thesaid armature l which is of elongated form is enlarged toreceive aneedle or stylus 8 and is clamped between rubber strips or in a tube ofrubber (as in the previous embodiments) held under pressure so as to beflattened between the polar extensions 6 by means of screws as at M." Awinding it! produces an electromotive force when the armature vibratesbetween the pole tips. Conversely currents fed to this coil will set upvibration in the armature. A split casing or cover 93 and 94 of whichthe part 94 alone is shown in Figure 27 grips the magnetic structure andholds it rigid by means of four screws passing through holes as at 95.

Figure 28 clearly shows the split casing 93 and 94 the pole tips II andthe usual swinging arm 52'corresponding to the tone arm of a gramophone.The clamped rubber between the polar extensions 6 constitutes a dampingchannel for progressively annulling transverse vibration as it travelsalong the armature strip, which in this case may be. for exampleone-eighth of an inch wide and one thirty second of an inch thick andmade from tool steel.

It will of course be appreciated that although, for the sake ofsimplicity and convenience pickups only have been illustrated a pick-upand a recorder are essentially reversible devices in the energyconversion sense just as an electric motor and an electric generatorare. Thus a pick-up can be used as a recorder and vice versa without anychanges of a fundamental nature 1. e. without any changes other than ofobvious design details such as substituting for a needle (for pickingup) a cutter (for recording). In fact it is possible in carrying outthis invention to provide a single embodiment adapted to serve bothpurposes; e. g. the armature of the embodiment of Figure 1 might beprovided with a stylus holder and a cutter side by side thereon. Withsuch an arrangement the embodiment would be used in a tiltedposition-tilted in one direction so that the stylus engaged a record forpicking up and tilted in the other so that the cutter engaged the recordfor recording. Such a dual purpose device would be very useful, forexample, for use in offices to enable dictation to be recorded andafterwards reproduced for a typist.

In the claims which follow the expression electro-acoustic recordtranslator is employed in a wide sense to include a device which isadapted to translate acoustic frequency electric currents intophonograph or gramophone sound records or to translate phonograph orgramophone sound records into acousticfrequency elec- The tric currents,or both. Similarly the term record, engaging member includes either astylus or a cutter.

What I claim is: V 7 r 1. In an electro-acoustic record translator, anelastic armature which is long relative to its width and thickness, saidarmature being sufficiently flexible totransmit acoustic frequencytransverse Waves along its length if transversely vibrated at acousticfrequency at or near one end, a record engaging member operativelyassociated with said armature at or near said one end thereof, means forsmoothly and gradually damping out said transverse waves comprisingresilient damping material in pressure contact with those opposite sidesof said armature which include the length and width dimensions thereof,said damping material extending over not less than about one-half thelength of said armature but not as far as the said end thereof, andenergy converting means for translating vibratory movement of said endof said armature into acoustic frequency electric currents and viceversa.

2. In an electro-acoustic record translator, an elastic armature whichis long relative to its width and thickness, said armature beingsufiiciently flexible to transmit acoustic frequency transverse wavesalong its length if transversely vibrated at acoustic frequency at ornear one end, a record engaging member operatively associated with saidarmature at or near said one end thereof, means for smoothly andgradually damping'out said transverse Waves comprising resilient dampingmaterial in pressure contact with those opposite sides of said armaturewhich include the length and width dimensions thereof, said dampingmaterial extending over not less than about one-half the length of saidarmature but not as far as the said end thereof, and energy convertingmeans for translating vibratory movement of said end of said armatureinto acoustic frequency electric currents and vice versa, said armaturebeing supported solely through the intermediary of said dampingmaterial. 5

3. A device according to claim 1 and further characterized in that thedamping material is in the form of two strips of rubber one on each sideof the armature.

4. A'device according to claim 1 and wherein the damping material whichforms the sole support'for the armature is in the form of two strips ofrubber one on each side of the armature.

5. In an electro acoustic record translator, an elastic armatureconstituted by a ferro-magnetic blade which is longrelative to its widthandthickness, said armature being sufficiently flexible to transmitacoustic frequency transverse Waves along its length if transverselyvibrated at acoustic frequency at or near one end, a record engagingmember operatively associated with said armature at or near said one endthereof, means for smoothly and gradually damping out said transversewaves comprising resilient damping material in pressure'contact withthose opposite sides of said armature which include the length andwi'dthdimensions thereof, said damping material extending over not less thanabout onehalf the length of said armature butnot as far as. the said endthereof, and ele'ctro-magnetic energy converting means including amagnet system having at least one air gap with which said armature endis operatively associated for translating vibratory movement of said endof said armature into acoustic frequency electric currents and vicevversa,.

6. In an electro-acoustic record translator, an"

elastic armature constituted by a ferro-magnetic blade which is longrelative to its width and thickness, said armature being sufiicientlyflexible to transmit acoustic frequency transverse waves along itslength if transversely vibrated at acoustic frequency at or near oneend, a record engaging member operatively associated with said armatureat or near said one end thereof, means for smoothly and graduallydamping out said transverse waves comprising resilient dampingmaterialin pressure contact with those opposite sides of said armature whichinclude the length and width dimensions thereof, said damping ma terialextending over not less than about onehalf the length of said armaturebut not as far as the said end thereof, and electro-magnetic energyconverting means including a magnet system having at least one air gapwith which said armature end is operatively associated for translatingvibratory movement of said end of said armature into acoustic frequencyelectric currents and vice versa, said armature being supported solelythrough the intermediary of said damping material.

,7. In an electro-acoustic record translator, an elastic armatureconstituted by a ferro-magnetic blade which is long relative to itswidth and thickness, said armature being sufficiently flexible totransmit acoustic frequency transverse waves along its length iftransversely vibrated at acoustic frequency at or near one end, a recordengage ing member operatively associated with said armature at or nearsaid one end thereof, means for smoothly and gradually damping out saidtransverse Waves comprising resilient damping material in pressurecontact with those opposite sides of said armature which include thelength. r

and width dimensions thereof, said damping material extending over asubstantial length of said armature but not as far as the said endthereof, and electro-magnetic energy converting means including a magnetsystem having at least one air gap with which said armature end isoperatively associated for translating vibratory movement of said end ofsaid armature into acoustic frequency electric currents and vice versa,a plate for clamping said armature and said damping material to a fiatface on said magnet, said armature being supported solely through theintermediary of said damping material by'clamping said armature by saidclamp plate through said material against said fiat face of said magnet,there being a portion of said material between said clamp plate and saidarmature and a portion between said armature and said flat face of saidmagnet. V 7

8. A translator in accordance with claim 1 and wherein the dampingmaterial is inthe form of a tube in which said armature is inserted.

9. A translator in accordance with claim'2 and wherein the dampingmaterial is in the form of a tube in which said armature is inserted.

10. A translator in accordance with claim 7 and wherein the dampingmaterial is in the form of a tube in which said armature is inserted.

11. In an electro-acoustic record translator, an elastic armatureconstituted by a ferro-magnetic blade which is long relative to itswidth and thick: ness, said armature being sufiiciently flexible totransmit acoustic frequency transverse waves along its length iftransversely vibrated at acous' tic frequency at or near one end, arecord engaging member operatively associated with said armature at ornear said one end thereof, means for smoothly and gradually damping outsaid transverse waves comprising resilient damping material in pressurecontact with those opposite sides of said armature which include thelength and width dimensions thereof, said damping material extendingover not less than about one-half the length of said armature but not asfar as the said end thereof, and electro-magnetic energy convertingmeans including a magnet system having at least one air gap with whichsaid armature end is operatively associated, said magnet having a poleadjusting screw member passing through a limb thereof in the directionof said armature for translating vibratory movement of said end of saidarmature into acoustic frequency electric currents and vice versa.

12. A translator in accordance with claim 1 and wherein the armature isformed to carry the record engaging member at or near its undamped end.

13. A translator in accordance with claim 7 and wherein the armature isformed to carry the record engaging member at or near its undamped end.

14. A translator in accordance with claim 1 and wherein the armature isformed to carry the record engaging member at or near its undamped end,said member extending at right angles to the length and width of saidarmature.

15. A translator in accordance with claim 1 and including a transmissionlink for operatively connecting the armature to the record engagingmember, a housing, means for pivotally mounting the record engagingmember in the housing and means for mounting the housing for movementswith respect to the main body of the translater.

16. A translator in accordance with claim 1 and including atransmission. link constituted by a chain knotted cord member foroperatively connecting the armature to the record engaging member, ahousing, means for pivotally mounting the record engaging member in thehousing, and means for mounting the housing for movements with respectto the main body of the translator.

ADRIAN FRANCIS SYKES.

